Re: GQRP - HF9 TRF Rx - Sprat 82


From: David Taylor (
Date: Fri Aug 11 1995 - 07:17:38 EDT

Dave, NF0R writes to G QRP-L (and I'm directing to QRP-L) ...

>Wondering if builders of the HF9 TRF Short Wave Receiver in Sprat 82
>would kindly share their experiences?

I haven't built a regenerative Rx but also looked up the Sprat article
after the recent discussions on basic receivers. Certainly Keith's
(G0KJK) approach to assembling a station is noteworthy given the
focus of this list. Paraphrasing from the article:-

Keith uses the HF9 both as his main station Rx and with a portable
station. His transmitter is also homebrewed and QRP. The HF9 uses
four transistors - a FET as the regenerative detector and three NPN
transistors as audio amplifiers. It is powered by a 7.2V Nicad pack,
built on a 20 way tagstrip and uses three switched toroidal coils to
cover the nine HF amateur bands from 160 to 10 metres.

The single tuned circuit is tuned by a 150pF variable cap with a 5pF
variable cap for bandspread tuning. SSB and CW are resolved with the
detector just oscillating and Keith claims to have heard ZL4BO on 40m
with a 10' length of wire lying on the floor! (But then, I've heard ZL4BO
by mixing his signal with the Nth harmonic of the crystal in my watch
in a rusty downpipe joint and listening to the open end as the metal
vibrates in the earth's magnetic field! No kidding! ZL4BO is in the same
region though).

Seriously, I imagine the Regen Rx would probably perform like a DC Rx
with a very wide audio filter and with the fiddliness of the regen
control thrown in. That raises a point - sophisticated designs for
audio filters and low noise amplifiers exist (KK7B's R1/R2 for eg) -
I wonder if performance would be improved by using a regen detector
in front of an R1 audio channel?

I have an R2 on my bench - all I need to do to test the idea is build
the regen detector - hmmm!

>73 from St. Louis, Missouri is the USA where it is 97F. Good excuse to
>stay inside and build this project.
>Dave, NF0R #2588

The sun has just come out here after 4 weeks of dull skies and rain - don't
we get sick of whatever wx we get when it goes on too long?

73/72 from wintery Melbourne, Australia

David Taylor Amateur Radio: VK3JKP
Computer Centres CW Ops QRP Club (Aus) No 423
RMIT (Bundoora Campus) G QRP Club No 8937
Melbourne 3083 Australia Internet:

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